1. Field of the Invention
The present invention relates to a robot hand for high load work, more particularly relates to a robot hand able to perform high load screwing work or high load calking work or press-fitting work when using a small tabletop robot for assembly work.
2. Description of the Related Art
As a first related art, Japanese Unexamined Patent Publication (Kokai) No. 7-171643 discloses an industrial robot hand using an air cylinder supported by a frame of a robot hand to drive a hammer and strike part of a thick steel plate formed in advance with a part cut along a target shape so as to punch out the target part of the steel plate, where, so as to raise the effect of striking and reduce the number of strikes and so as to prevent the reaction force occurring due to the striking action of the hammer from being transmitted to the robot arm supporting the robot hand, electromagnets able to hold the steel plate are used to affix the steel plate to the frame of the robot hand and shock absorbing springs are attached to the parts connecting the frame to the robot arm.
Further, as a second related art, Japanese Unexamined Patent Publication (Kokai) No. 2000-296421 discloses a system enabling simultaneous machining such as drilling by a drill supported by a robot arm on a line performing plasma processing or laser processing by attaching to a mounting base supported at a front end of the robot arm not only a working tool for the machining, but also a holding tool, and holding a workpiece by the holding tool so as have the reaction force of the working force be received by both the workpiece and the holding tool and thereby enable high accuracy machining. As examples of a holding tool in this case, it discloses to use electromagnets or a vacuum suction holding device for holding the workpiece or a hook mechanism for mechanically engaging with the workpiece.
The above first related art relates to work for punching out a piece of a steel plate by the striking action of a hammer, while the second related art illustrates the work of drilling a hole in a steel plate by a drill, so these disclosed related art can be said to be related to the work of forming holes. Therefore, only naturally, even if these related art were applied to a robot hand for screwing work, which is completely different work from hole-forming work, it would not be possible to have the torque occurring due to the screwing and the reaction torque be canceled out inside the robot hand and prevent the transmission of torque to the robot arm, robot base, etc. If not able to cancel out the large torque occurring due to screwing inside the robot hand, the torque would be transmitted to the structural parts of the robot body and cause those parts to elastically deform, so if the main structure is low in rigidity, the position of the robot hand could no longer be accurately controlled.
Further, since the above-mentioned first related art and second related art both relate to work for forming holes, even if these related art were applied to a robot hand for calking work or press-fitting work, which again are completely different from hole-forming work, it would not be possible to have the action force for such work and the reaction force occurring due to this be canceled out inside the robot hand and prevent the transmission of the action force to the robot arm or robot base etc. If not able to cancel out the large action force applied for the calking work or press-fitting work inside the robot hand, the action force would be transmitted to the structural parts of the robot body and cause those parts to elastically deform, so the same problem as with the above screwing work would arise.
Generally speaking, screwing work, calking work, and press-fitting work fall under the category of high load work, so to prevent position control of the robot hand from being impaired even if a large torque due to the screwing work or a large action force due to the calking work or press-fitting work is transmitted to the robot body, it becomes necessary to use a large sized robot system having a robot arm, robot base, etc. having an extremely high rigidity. Therefore, when using a small-sized robot system such as a tabletop robot designed for assembly work of auto parts so as to perform screwing work, calking work, or press-fitting work along with part assembly work, the large torque or action force due to these high load work would act on the robot arm or other low rigidity parts to cause them to elastically deform, so the accuracy of positioning of the robot hand would drop. Therefore, a low rigidity robot system generally cannot be used to reliably perform screwing work, calking work, or press-fitting work as ancillary work in an assembly process etc.
Further, in the above-mentioned two related art, the workpiece is mainly held by the action of electromagnets, but when the workpiece is a nonmagnetic metal material or plastic material often used in auto parts, the electromagnetic means of holding the workpiece is ineffective. Therefore, in this sense as well, it can be said to be impossible to apply the above related art to screwing work, calking work, or press-fitting work.